High-Symmetry Magnonic Modes In Antidot Lattices Magnetized Perpendicular To The Lattice Plane

Microwave magnetization dynamics on two-dimensional periodic arrays of nanoscale magnetic antidots with magnetic field applied perpendicular to the lattice plane have been studied using ferromagnetic resonance spectroscopy. Linear dependence of the resonant mode frequency on the applied field was observed experimentally. Theoretical calculations show that this linear dependence originates from the high symmetry imposed by applying the field perpendicular to the plane of the antidot lattice. The calculated mode profiles exhibit a fourfold symmetry in contrast to the twofold symmetry typical for the in-plane magnetization direction. From the calculated Bloch wave dispersion the group velocities along the [10] and [11] directions and close to the center of the first Brillouin zone are found to be the same, which demonstrates a very high degree of isotropy of magnonic modes for the center of this zone in this case. Perpendicular standing spin-wave modes due to microwave shielding were also observed on the antidot lattices.